Money

Wizard MoneyThere are three basic
types of coins in the wizarding world:

gold Galleon

silver Sickle

bronze Knut

The Galleon has numerals around the outside edge which is a serial number
referring to the Goblin who cast the coin. It is unknown whether the
Sickle or Knut also have these numbers, but it seems likely.

The actual values of these coins are a bit complicated for Muggles to figure
out in Muggle terms without a calculator, and rather difficult for wizards
when dealing with Muggle money (GF7).
It's easy for wizards dealing only with wizarding currency, however. Hagrid
states: "The gold ones are Galleons. Seventeen silver Sickles to a
Galleon and twenty-nine Knuts to a Sickle, it's easy enough." Therefore
1 Galleon = 17 Sickles = 493 Knuts.

Well, even if you can do
the math quickly in your head when you need to make change, it's still
not easy. The values of the coins don't always seem to make sense. After
all, you can buy a large quantity of sweets from the cart on the Hogwarts
Express for eleven Sickles, about two-thirds of one Galleon. So is that
all that the Weasleys had in their vault? The price of a pile of candy?
And with that they bought books and school gear for all those kids? It
just doesn't quite work out.

JKR has stated in an interview (CR)
that she estimates the value of one Galleon to be "about five pounds,"
which works out to around US$9.75 (the exchange rate at the time of the interview was US$7.33). In the introduction to both QA
and FB, US$250-million is stated to be the equivelent of 34 million Galleons.
That also works out to a value of £5 to the Galleon, at the exchange rate of the time. The price listed
on the back of the books, however, is not correct, since US$3.99 would
equal less than half a British pound, or 8 sickles and 15 knuts.
The book instead incorrectly lists US$3.99 as being equal to 14 sickles
and 3 knuts. (Unfortunately, CNN.com uses this incorrect value for their
Knuts-to-dollars
converter.)

There is apparently some kind of foreign wizard money that
consists of gold coins the size of hubcaps (if Mr. Roberts wasn't simply
giving an exaggerated description of Galleons)
(GF7).

While wizard money seems to be made from actual precious metals, it also
seems to have some sort of magic in it which makes it lighter than normal.
Harry handled a bag containing one thousand Galleons-- the prize money from
the Triwizard Tournament--as
if it were nothing, but a thousand coins made out of gold, even fairly
small ones, would weigh a considerable amount indeed, far more than anyone
would be able to toss around in a cloth bag. This magic is perhaps an effect
similar to Wizard Space.

dragon liver
(PS5, corrected edition)
.....16 Sickles per ounce
Originally this passage read seventeen Sickles, but notice that
that would equal 1 Galleon, so a witch would be unlikely to give the
amount in Sickles. That's why the passage was changed for later editions.

pile of candy from the cart on the Hogwarts Express
.....11 Sickles, 7 Knuts

fare on the Knight Bus from
Little Whinging to London
(PA3)
.....11 Sickles

Hit-Witch or Hit-Wizard for the Magical Law Enforcement Squad
(new hire's starting salary, together with a
Ministry of Magicbroomstick and one's own regular
bed at St. Mungo's)
(DP)
.....700 Galleons per month